1. Field of the Invention
The present invention relates to an automatic transmission system having an automatic transmission apparatus and a method for controlling the automatic transmission apparatus.
2. Description of Related Art
An electric shift range change apparatus, which changes a shift range change mechanism of an automatic transmission apparatus through use of an electric actuator, has been proposed (see, for example, Japanese Unexamined Patent Publication No. H03-186657 and Japanese Unexamined Patent Publication No. 2004-56858 corresponding to US2003/0222617A1 and US2006/0033464A1).
In this electric shift range change apparatus, there is no mechanical connection between a shift range setting device, i.e., a shift range setting means (e.g., a mechanical shift lever operated switch, a shift range setting button, a joystick) and a shift range change mechanism (a mechanism that mechanically slides a manual spool valve, which changes a hydraulic pressure according to a shift range at hydraulic pressure controller). Thus, there is a high degree of freedom in terms of positioning of the shift range setting device and the shift range change mechanism in the vehicle.
Furthermore, since there is no mechanical connection between the shift range setting device and the shift range change mechanism, the shift range setting device can be freely designed regardless of the structure of the shift range change mechanism. Thus, it is possible to design the easy-to-operate shift range setting device in view of the ergonomics. Furthermore, the user may possibly replace the current shift range setting device with a more appropriate shift range setting device based on the situation.
The SBW controller controls the electric actuator based on the range demand value, which is outputted from the shift range setting device, to change the actual shift range.
The SBW controller is an electronic controller, which needs electric power for its operation. Thus, an instantaneous power interruption or failure (an instantaneous stop of the power supply) of the SBW controller may possibly occur due to some unexpected reason (e.g., unexpected electrical contact malfunctioning).
In the case of the mechanical shift range change apparatus, which changes the shift range of the automatic transmission apparatus through a mechanical transmission mechanism, such as a wire, a rod, the selected shift range, which is set by the occupant through the shift range setting device (a mechanical shift lever), reliably coincides with the actual shift range of the shift range change mechanism.
However, in the case of the electric shift range change apparatus, there is no mechanical connection between the shift range setting device and the shift range change mechanism, as described above. Thus, when the power supply of the SBW controller is instantaneously interrupted, and thereby the SBW controller is restarted, it may possibly happen that the SBW controller cannot correctly recognize the actual shift range.